1. Field of the Invention
The present invention relates to a high voltage power supply (HVPS) of an image forming apparatus and a method for controlling the HVPS. More particularly, the present invention relates to an analog control application specific integrated circuit (ASIC) apparatus for an HVPS in an image forming apparatus.
2. Description of the Related Art
FIG. 1 is a control block diagram of a high voltage power supply (HVPS) for one output. The HVPS for one output includes a pulse width modulation (PWM) input unit 100, a low pass filter (LPF) 110, a voltage controller 120, an oscillator 130, a transformer 140, a voltage doubler 150, and a feedback unit 160. FIG. 2 is an illustration of a circuit diagram of FIG. 1.
The PWM input unit 100 receives a PWM input signal of several KHz, and an output voltage level is determined according to a duty ratio of the PWM input signal. The LPF 110 converts the PWM input signal to a DC signal using an RC two-stage filter, and the converted DC signal is used as a reference signal for controlling an output voltage. The voltage controller 120 operates as a differential circuit and a controller in which an error signal is amplified based on the output voltage reference signal output from the LPF 110 and a voltage sensor signal to detect an actual feedbacked output voltage. The oscillator 130 changes a voltage between an emitter and a collector of a transistor by controlling a magnitude of a base current of the transistor based on an output of the voltage controller 120. When the voltage between the emitter and the collector of the transistor in the oscillator 130 is changed, a voltage of the primary winding of the transformer 140 connected to the oscillator 130 in series is changed. Then an output voltage is induced due to a high turn ratio. The voltage doubler 150 generates a final DC high voltage from a secondary voltage of the transformer 140 using a voltage doubling circuit including a diode rectifier and capacitors. The feedback unit 160 is a protect circuit sensing the final DC high voltage, distributing the output voltage through a resistor, and preventing an abnormal voltage from being applied.
As described above, many components should be assembled to construct the analog control unit in the primary side of the transformer 140. That is, the analog control unit is constructed with resistors, capacitors, transistors, integrated circuits (ICs), and diodes as shown in FIG. 2. FIG. 3 is an example of a conventional analog control unit of the HVPS. Since there are a number of components, the number of procedures and a working time increase in an assembly process, and a printer circuit board (PCB) space should be prepared. In addition, an output voltage may be distorted due to a characteristic deviation between the components, and a unit component may be rendered defective due to an outside cause.
Accordingly, there is a need for an improved high voltage power supply in an image forming apparatus with reduced components.